1. Technical Field
The present invention relates to a cable-type secondary battery of free shape adaptation, and more particularly, to a cable-type secondary battery with a coating (cover member) of an improved structure surrounding a cable-type electrode assembly.
2. Background Art
Recently, advances in wireless communication technologies have led to the popularization of mobile devices, and to keep pace with this trend, there is a strong tendency to use secondary batteries as a power source of mobile devices. Secondary batteries are also used as a power source of environmentally friendly next-generation vehicles such as electric vehicles and hybrid vehicles.
As described above, as the use of secondary batteries is dramatically increasing in many fields of industry, secondary batteries are varying in output, capacity, structure, and the like, depending on the characteristics of the field where the secondary batteries are used.
Generally, a secondary battery is provided with an electrode assembly including a cathode and an anode, each having a plate-like current collector surface-coated with an active material, and a separator interposed between the cathode and the anode. The electrode assembly is received in a cylindrical or prismatic metal casing or a pouch-type casing of an aluminum laminate sheet, together with a liquid electrolyte or a solid electrolyte. To improve the capacity of the secondary battery, the electrode assembly may be a jelly-roll type in which a cathode sheet, a separator sheet, and an anode sheet are rolled together, or a stack-type in which a plurality of unit electrodes of a thin plate shape are sequentially stacked. Accordingly, the electrode (cathode and anode) of the electrode assembly has a substantially plate-like structure.
The conventional plate-like electrode structure is advantageous in that it has a high degree of integration when rolling or stacking, but has difficulty in adaptively changing the structure to meet the demand of the industrial field. Furthermore, the plate-like electrode structure has various problems in that it is sensitive to the change in volume of the electrode during charging/discharging, the gas generated in the cell may not easily discharge, and the potential difference between the electrodes may increase.
Particularly, to meet the various needs of the users, the kinds of devices using secondary batteries are diversifying and a lot of emphasis is put on designing such devices. However, devices having a special shape need to offer a separate portion or space for mounting secondary batteries having a traditional structure and/or shape (cylindrical, prismatic, or pouch-type), which becomes a great obstacle when expanding the wireless technologies and developing new designs. For example, when a newly developed device has an elongated space for mounting a secondary battery, it is substantially impossible or very inefficient to structurally change the secondary battery including an electrode assembly made up of existing plate-like electrodes to suit the structure to the mounting space. In other words, since the conventional cylindrical, coin-type, and prismatic batteries have specific shapes, the batteries are limited in its use and ability to freely deform. Accordingly, it is difficult to adaptively deform, for example, twist or bend, depending on where the batteries are used.
To solve these problems, the inventors have disclosed Korean Patent No. 10-0804411 (filed Jan. 17, 2006, registered Feb. 12, 2008) titled “electrode assembly of novel structure and secondary battery comprising the same”.
However, this secondary battery (hereinafter referred to as a cable-type secondary battery) still has insufficient flexibility. Also, when a cable-type secondary battery is deformed by an excessive external force, an active material may fall off from an active material layer.